Particle beam treatment apparatus

ABSTRACT

A particle beam treatment apparatus includes: a rotating gantry configured to axially rotate in a state where a bed fixed to a stationary system is disposed inside the rotating gantry and an irradiation port of a beam is fixed to a body of the rotating gantry; a tunnel structure configured to have at least a horizontal floor surface and have an internal space in which at least a part of the bed is accommodated; and a rotation supporter configured to cause the tunnel structure to be stationary in the stationary system independently of axis rotation of the rotating gantry by rotationally displacing the tunnel structure with respect to an inner side surface of the rotating gantry.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional and claims priority to U.S. applicationSer. No. 15/988,611 filed May 24, 2018, and claims the benefit ofpriority of Japanese Patent Application No. 2017-107399, filed May 31,2017, the entire contents of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments described herein generally relate to a particle beamtreatment apparatus equipped with a rotating gantry.

Description of the Related Art

A particle beam therapy is widely practiced as treatment of irradiatinga particle beam such as a proton beam and a carbon ion beam onto alesion area (e.g., cancer) of a patient. As one of such particle beamtherapies, there is a known technique in which a patient lying on atreatment bed is positioned and irradiated with a particle beam in atreatment room formed inside a large rotation mechanism (hereinafterreferred to as a rotating gantry).

Such a particle beam treatment apparatus equipped with a rotating gantryirradiates a particle beam onto a lesion area of a patient from anarbitrary direction by rotating an irradiation port fixed to therotating gantry and/or displacing the treatment bed in the treatmentroom.

The treatment room formed inside the rotating gantry is formed with amoving floor which is composed of a horizontal and flat floor surfaceand the other surface in the form of an arch along the innercircumference of the rotating gantry, regardless of the rotationposition of the rotating gantry.

Additionally, the irradiation port penetrate the opening of the movingfloor, and the moving floor is caused to fully rotate in synchronizationwith rotation of the rotating gantry. Further, there is provided afunction of adjusting the size of the opening of the moving floor andfilling the gap with the penetrating irradiation port, corresponding tothe rotational position of the irradiation port. If this gap is large,it becomes difficult for a technician to access the bed and increasesthe risk of falling of a utensil or the like to the outside of thetreatment room, so the above function is provided.

PRIOR ART

Patent Document 1; Japanese Unexamined Patent Application PublicationNo. 1999-47287

Patent Document 2; Japanese Unexamined Patent Application PublicationNo. 2001-353228

Patent Document 3; Japanese Unexamined Patent Application PublicationNo. 2011-156263

Since the treatment room is formed with the moving floor which maintainsthe horizontal flat floor surface and the arch surface while rotating afull axial rotation (i.e., ±180°), it is possible to improve workabilityof a technician in the internal space of the treatment room and toreduce oppressive feeling of a patient lying on the treatment bed.

However, when the treatment room is formed with such a moving floor, themechanical rigidity of the moving floor is required to a certain degreeand thus it is not possible to take a wide space of the treatment roomespecially in the rotational axis direction. For this reason,improvement in workability of a technician and reduction in oppressivefeeling of a patient are insufficient.

As to the function of adjusting the size of the opening of the movingfloor, in conventional technology, there is a problem that noise isgenerated due to rubbing of contact surfaces of a slide couplingmechanism to be adopted and application of this function is restricted.

In view of the above-described problems, it is an object of embodimentsof the present invention to provide a particle beam treatment apparatuswhich has a wide treatment space and is excellent in general versatilityand robustness.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1A is an X-Y cross-sectional view of the particle beam treatmentapparatus according to the first embodiment of the present invention;

FIG. 1B is an Y-Z cross-sectional view of the particle beam treatmentapparatus according to the first embodiment;

FIG. 2A is a perspective view illustrating the appearance of theparticle beam treatment apparatus of each embodiment;

FIG. 2B is an overall perspective view of a moving floor and a tunnelstructure of the particle beam treatment apparatus of each embodiment;

FIG. 3A and FIG. 3B are schematic diagrams illustrating an operation(i.e., movement) of the moving floor applied to the second embodiment;

FIG. 4A and FIG. 4B are schematic diagrams illustrating the operation(i.e., movement) of the moving floor applied to the second embodiment;

FIG. 5A is a side view illustrating a connecting portion of plates ofthe moving floor applied to the third embodiment;

FIG. 5B is a top view illustrating the connecting portion of the platesof the moving floor; and

FIG. 5C is a side view illustrating the connecting portion of the platesof the moving floor in the state of being bent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereinbelow, embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 1A and FIG. 1B are an X-Y cross-sectional view and an Y-Zcross-sectional view of the particle beam treatment apparatus 10 of thefirst embodiment, respectively.

FIG. 2A is a perspective view illustrating the appearance of theparticle beam treatment apparatus 10.

As shown in FIG. 1A, FIG. 1B, and FIG. 2A, the particle beam treatmentapparatus 10 includes a rotating gantry 15, a tunnel structure 16, and arotation supporter 57. The rotating gantry 15 axially rotates in a statewhere a bed 24 fixed to a stationary system is disposed inside therotating gantry 15 and an irradiation port 18 of a beam 19 is fixed tothe body of the rotating gantry 15. The tunnel structure 16 has ahorizontal floor surface and an arch-shaped ceiling, and is providedwith an internal space in which at least a part of the bed 24 isaccommodated. The rotation supporter 57 causes the tunnel structure 16to be stationary in the stationary system regardless of the axisrotation of the rotating gantry 15, by rotationally displacing thetunnel structure 16 with respect to an inner side surface 15 a of therotating gantry 15.

The particle beam treatment apparatus 10 further includes a moving floor12 which is formed by joining multiple plates 11 (FIG. 2B) in thecircumferential direction to each other such that the moving floor 12 isbendable as a whole and the internal space from the tunnel structure 16becomes continuous. The moving floor 12 rotates about the Z-axis (i.e.,the central axis of the rotating gantry 15) together with the rotatinggantry 15 in a state where the irradiation port 18 penetrates the movingfloor 12.

As shown in FIG. 2A, the rotating gantry 15 is generally a large-sizedstructure having a cylindrical shape and rotates about the rotationalaxis (i.e., Z-axis) under rotation driving of plural rotation drivers23, which are in contact with the respective ring-shaped outerperipheral surfaces of both ends of the rotating gantry 15. Weight ofthe rotating gantry 15 is supported by foundations 21 via the rotationdrivers 23.

The rotating gantry 15 rotates about the Z-axis in a state where the bed24 fixed to the stationary system is disposed inside and the irradiationport 18 of the beam 19 is fixed to the body thereof.

The rotating gantry 15 is provided with many other controllers andstructures such as a beam transport system 27 and a deflectionelectromagnet 28 of a beam in addition to the irradiation port 18 of theparticle beam 19.

The particle beam 19 is formed by accelerating ions (i.e., heavyparticles or proton ions generated by a non-illustrated ion source) witha linear accelerator and then making the accelerated ions incident on anon-illustrated circular accelerator to increase the energy of the ionsto a preset value.

The beam transportation system 27 is provided so as to rotate integrallywith the rotating gantry 15, and the particle beam outputted from thecircular accelerator is made incident on the beam transportation system27 from the extension line of the rotation axis Z of the beamtransportation system 27.

The irradiation port 18 is inserted toward the inside of the rotatinggantry 15 and rotates together with the rotating gantry 15 by ±180°around the bed 24.

The trajectory of the particle beam made incident on the beam transportsystem 27 is bent by the deflection electromagnet 28, and then theparticle beam is irradiated onto a patient lying on the bed 24 in anydirection of 0° to 360° from the irradiation port 18.

The bed 24 has a base fixed to the foundation of the building side,moves inside the rotating gantry 15, and positions a lesion area of apatient at the irradiation position of the particle beam 19.

After the particle beam 19 is irradiated towards the lesion area, theparticle beam 19 decreases its speed by losing kinetic energy whenpassing through the patient's body, and suddenly stops when it falls toa certain speed by receiving a resistance which is approximatelyinversely proportional to the square of speed.

In the vicinity of the stop point of the particle beam 19, high energycalled a Bragg peak is emitted. Since the bed 24 is positioned such thatthe release position of this Bragg peak coincides with the lesion area,only the tissues of the lesion area are killed and treatment with lessdamage of normal tissues is executed.

FIG. 2B is a schematic perspective view focusing on the moving floor 12and the tunnel structure 16. Each of the plates 11 constituting themoving floor 12 is desired to have large flexural rigidity in thelongitudinal direction and to be lightweight. The multiple plates 11 arejoined to each other at the side edge portions thereof.

Since a part of the moving floor 12 is formed as an opening and theirradiation port 18 is fixed to the rotating gantry 15, the moving floor12 can rotate in conjunction with (i.e., in synchronization with) therotation of the rotating gantry 15 by causing the irradiation port 18 topass through the opening.

As a form of the moving floor 12, in addition to the case of forming asingle sheet in an annular shape, plural separate bodies and sheets ofthe respective separate bodies are formed in a annular shape incombination in some cases as described below in the second embodiment.

As shown in FIG. 1B, a first rail 13A and a second rail 13B are slidablyengaged at one end and the opposite end of the moving floor 12,respectively. Each of the first rail 13A and the second rail 13B has aclosed track composed of a circular arc and a straight line (FIG. 1A).Thus, the inner space of the moving floor 12 forms a tunnel shapesurrounded by a flat horizontal floor and an arch-shaped ceiling, andthe moving floor 12 can rotate about the rotation axis Z while keepingthe tunnel shape stationary.

The moving floor 12 does not have to be wide in the direction of therotation axis (i.e., Z-axis direction) because space of the treatmentroom is sufficiently secured due to the presence of the tunnel structure16 described below. Hence, the moving floor 12 can be designed to belightweight and have high mechanical rigidity, and thus the rotarymotion of the moving floor 12 can be smoothly implemented whilemaintaining quietness.

The first rail 13A is supported at one end of a hollow body 53, theother end of which is connected to an opening of a vertical wall surface(stationary system) 60 of the foundation 21 fixing the bed 24.

The support of the first rail 13A from the foundation 21 is not limitedto the illustrated method. For instance, the first rail 13A may be fixedto a non-illustrated supporting portion, which is rotatably providedwith respect to the inner peripheral surface of the rotating gantry 15and is supported by the vertical wall surface (stationary system) 60 ofthe foundation 21, in such a manner that the first rail 13A isindirectly supported by the stationary system.

The second rail 13B is fixed to the periphery of the tunnel structure 16which substantially matches in sectional shape with the second rail 13B.The second rail 13B is disposed so as to face the first rail 13A withthe irradiation port 18 interposed between the first and second rails13A and 13B, and is engaged with the other end of the moving floor 12.

It is sufficient that the distance between the first and second rails13A and 13B is slightly wider than the width of the irradiation port 18interposed between them.

By reducing the length of the moving floor 12 in the direction of therotation axis (Z-axis) in the range satisfying the above condition, bothof weight reduction and improvement of mechanical rigidity can beachieved for the moving floor 12 rotating together with the rotatinggantry 15.

The moving floor 12 can be omitted in some cases, e.g., in the casewhere the irradiation port 18 is further advanced and designed to have asmaller diameter and the gap between the hollow body 53 and the tunnelstructure 16 can be reduced to such an extent that there is no obstacleto the comings and goings of technicians.

Although the tunnel structure 16 having the horizontal floor and thearch-shaped ceiling is illustrated, the tunnel structure 16 issatisfactory when it has at least a horizontal floor surface andinternal space in which at least a part of the bed 24 is accommodated.

In the tunnel structure 16, a panel 51 is provided on the opposite sideof the second rail 13B so as to close the opening. The panel 51 issupported by a rotation shaft 52 of the rotation support portion 57which freely rotates. The position and orientation of the rotation shaft52 match the rotation axis Z of the rotating gantry 15.

The rotation supporter 57 rotationally displaces the rotation shaft 52which pivotally supports the tunnel structure 16 from a stand 56 fixedto the inner side surface 15 a of the rotating gantry. As a result, thetunnel structure 16 is stationary with respect to the stationary systemin such a manner that the flat floor surface always remains horizontalwithout depending on the rotational displacement of the rotating gantry15.

In the stationary system, the rotation shaft 52 of the rotationsupporter 57 is rotationally displaced in the direction opposite to therotational direction of the rotating gantry 15. As a result of therotation supporter 57 is fixed to the inner side surface 15 a of therotating gantry 15, thus the tunnel structure 16 is kept in thestationary state even when the irradiation port 18 rotates with respectto the stationary system.

Further, the rotation supporter 57 is provided with a support member 26which supports its own weight in the vertical direction. One end of thesupport member 26 is fixed to the tunnel structure 16 or the panel 51,and the other end of the support member 26 frictionlessly contacts theinner side surface 15 a of the rotating gantry 15 and rotates in thecircumferential direction. It should be noted that the rotation shaft 52of the rotation supporter 57 may be freely rotatable in addition tobeing driven and rotated by, e.g., a motor.

Although, a description has been given of the case where the rotationsupporter 57 is composed of the rotation shaft 52 and the stand 56 inthe present embodiment, the rotation supporter 57 is not limited to suchan aspect. In the present embodiment, it is possible to adopt anyrotation supporter 57 which can rotationally displace the tunnelstructure 16 with respect to the inner side surface 15 a of the rotatinggantry 15.

According to the above-described tunnel structure 16, it is possible toform a treatment room having a flat horizontal floor surface andsufficient room size inside the rotating gantry 15 without depending onthe rotational position of the irradiation port 18. This makes itpossible to improve the workability of a technician who accesses apatient lying on the bed 24.

Since the majority of this wide treatment room can be provided by thetunnel structure 16, the length of the moving floor 12 in the directionof the rotation axis can be shortened to substantially the same lengthas that of the irradiation port 18 which is the minimum length requiredin terms of its function. As a result, the moving floor 12 can befabricated with light weight and high rigidity or be omitted, and thusit is possible to provide a particle beam treatment apparatus in whichrobustness is enhanced and load of the rotation drive mechanism isreduced.

Second Embodiment

Next, a description will be given of the second embodiment of thepresent invention by referring to FIG. 3A, FIG. 3B, FIG. 4A, and FIG.4B. In FIG. 3A, FIG. 3B, FIG. 4A, and FIG. 4B, the same reference signsare assigned to the same components as those in FIG. 1 in terms ofconfiguration or function, and duplicate description is omitted.

The moving floor 12 applied to the particle beam treatment apparatus 10of the second embodiment is divided at the position where theirradiation port 18 penetrates, and is composed of at least two separatebodies 17A and 17B. The separate body (i.e., the first plate group) 17Aand the separate body (i.e., the second plate group) 17B respectivelyinclude traveling mechanisms 25A and 25B for independently traveling therespective closed tracks of the first and second rails 13A and 13B.

Specifically, a rack-and-pinion mechanism can be adopted as each of thetraveling mechanisms 25A and 25B. In this case, a motor for rotating asmall-diameter circular gear called a pinion is provided on the plate 11arranged at the center of each of the separate bodies 17A and 17B. Atleast one of the first rail 13A and the second rail 13B is provided witha toothed rack. When rotational force is applied to the combination ofthe rack and the pinion, the rotational force is converted into linearforce in the longitudinal direction of the rack, and the separate bodies17A and 17B of the moving floor 12 move along the respective closedtracks of the first and second rails 13A and 13B.

The traveling mechanisms 25A and 25B are not limited to therack-and-pinion mechanism and may be configured as any other mechanismas long as it can cause the separate bodies 17A and 17B to runindependently of each other on the closed track of the first and secondrails 13A and 13B.

The flat horizontal floor surface of the rotating moving floor 12 doesnot generate any gap and it is necessary to ensure the safety of thetechnicians coming and going. As can be seen by comparing FIG. 4A andFIG. 4B, the size of the opening of the moving floor 12 required tocause the irradiation port 18 to penetrate the moving floor 12 isdifferent depending on the rotational position of the irradiation port18. Thus, there is a circumstance that the side surface positions of theirradiation port 18 in contact with the respective edges of the separatebodies 17A and 17B change depending on the rotation position of theirradiation port 18.

Hence, the traveling mechanisms 25A and 25B for moving the separatebodies 17A and 17B are controlled such that any gap does not generatedon the flat horizontal floor surface when the respective edges of theseparate bodies 17A and 17B are located on the flat horizontal floorsurface. Specifically, the traveling mechanisms 25A and 25B arecontrolled such that the respective edges of the separate bodies 17A and17B are brought into contact with the irradiation port 18 or broughtinto contact with each other when being located on the flat horizontalfloor surface. As a result, anther opening is formed at the arch-shapedceiling on the opposite side of the flat horizontal floor by the gapbetween the respective edges of the separate bodies 17A and 17B, and thesize of this opening also changes depending on the rotational positionof the irradiation port 18 and the opening is permissible.

Since a gap is formed between the irradiation port 18 and the separatebody 17A, a shielding member 31A for shielding the formed gap isprovided. Similarly, another shielding member 31A is provided forshielding the gap between the irradiation port 18 and the separate body17B. Each of the shielding members 31A is provided with a roll 34 at theedge portion of the separate body 17A or 17B. Each shielding member 31Afurther include a sheet 33 wound around the roll 34, and the roll 34 isrotatably biased in the winding direction. The tip 32 of the wound sheet33 is connected to the side surface of the irradiation port 18. Itshould be noted that the attachment positions of the roll 34 and the tip32 of the sheet 33 may be reversed.

In this manner, the wound sheet 33 of each shielding member 31A expandsand contracts depending on the size of the gap formed between theirradiation port 18 and each of the separate bodies 17A and 17B so as toshield the gap.

Further, a shielding member 31B is also provided between the respectiveedge portions of the separate bodies 17A and 17B in the state of beingbutted to each other. The shielding member 31B includes the roll 34 andthe sheet 33 similarly to the shielding members 31A, and shields orfills the formed gap between the separate bodies 17A and 17B dependingon the size of the gap.

Specifically, on the side opposite to the irradiation port 18, the roll34 of the shielding member 31B is provided on one of the edge portionsof the two separate bodies 17A and 17B which are in close proximity toeach other while the tip 32 of the sheet 33 of the shielding member 31Bis connected to the other of the edge portions of the two separatebodies 17A and 17B.

In the second embodiment, the shielding members 31A and 31B are notindispensable components. In other words, the shielding members 31A and31B may be omitted when it is not important that the inner side surface15 a of the rotating gantry 15 is exposed from the opening of the movingfloor 12 formed on the arch side.

Consider a case where the rotation angle of the rotating gantry 15 isset to +180° and the irradiation port 18 is positioned directly underthe bed 24 as shown in FIG. 3A. In this case, by bringing theirradiation port 18 into contact with the respective edge portions ofthe separate bodies 17A and 17B, the horizontal flat floor surface ofthe moving floor 12 is formed without forming openings on both sides ofthe irradiation port 18.

Also in this case, each of the shielding members 31A provided on bothsides of the irradiation port 18 becomes the state in which the sheet 33extends between the base portion of the irradiation port 18 and the edgeportion of the separate body 17A or 17B.

Also in this case, the shielding member 31B at the butting position ofthe separate bodies 17A and 17B on the arch side becomes the state inwhich the sheet 33 extends in order to shield the formed gap.

Next, consider a case where the rotation angle of the rotating gantry 15is set to +135° and the irradiation port 18 is positioned obliquelybelow the bed 24 as shown in FIG. 3B. In this case, the edge of theseparate body 17A on the right side of the FIG. 3B reaches the base ofthe irradiation port 18. Also in this case, by bringing the respectiveedge portions of the separate bodies 17A and 17B into contact with theirradiation port 18, the horizontal flat floor surface of the movingfloor 12 is formed without forming an opening.

Further, consider a case where the rotation angle of the rotating gantry15 is set to +90° and the irradiation port 18 is positioned right besidethe bed 24 as shown in FIG. 4A. In this case, the respective edges ofboth separate bodies 17A and 17B reach the base of the irradiation port18. Also in this case, by bringing the respective edge portions of theseparate bodies 17A and 17B into contact with the irradiation port 18,the horizontal flat floor surface of the moving floor 12 is formedwithout forming an opening.

Under the state where the horizontal flat floor surface is formed asshown in FIG. 4A, each of the shielding members 31A provided on the sideof the irradiation port 18 becomes the state in which the sheet 33contracts between the base portion of the irradiation port 18 and theedge portion of the separate body 17A or 17B. Also under this state, theshielding member 31B at the butting position of the separate bodies 17Aand 17B on the opposite side becomes the state in which the sheet 33extends so as to shield the formed gap.

Further, consider a case where the rotation angle of the rotating gantry15 is set to 0° and the irradiation port 18 is positioned directly abovethe bed 24 as shown in FIG. 4B. In this case, by bringing the respectiveedge portions of both separate bodies 17A and 17B into contact with eachother on the horizontal floor surface, the horizontal flat floor surfaceof the moving floor 12 is formed without forming an opening.

Also in this case, the shielding member 31B positioned on the horizontalflat floor surface becomes the state in which the sheet 33 iscontracted, and each of the shielding members 31A provided on both sidesof the irradiation port 18 on the arch side becomes the state in whichthe sheet 33 is extended between the base portion of the irradiationport 18 and the edge portion of the separate body 17A or 17B so as toshield the generated gap.

The above-described positional relationship between the irradiation port18 and the separate bodies 17A and 17B and the expansion/contractionrelationship of the shielding members 31A and 31B are given as somepossible aspects, and the embodiments of the present invention are notlimited to such aspects. Thus, these relationships are appropriatelychanged depending on the arcuate orbit (i.e., track) of the first andsecond rails 13A and 13B, the length of the linear track, and/or thesize of the irradiation port 18. Although a description has been givenof a case where the rotating gantry 15 rotates in the range of +180° to0°, the rotating gantry 15 also rotates in the range of 0° to −180°.

Each of the rotating gantry 15 and the irradiation port 18 has a mirrorsymmetrical shape. Thus, even when the rotating gantry 15 rotates in therange of 0° to −180°, motions of the separate bodies 17A and 17B areappropriately controlled such that any opening is not formed on thehorizontal floor surface of the moving floor 12.

In the particle beam treatment apparatus 10 of the second embodiment, itis an essential requirement that the moving floor 12 is composed of theseparate bodies 17A and 17B and the separate bodies 17A and 17B areprovided with the respective traveling mechanisms 25A and 25B. Thus, theparticle beam treatment apparatus 10 without the tunnel structure 16and/or the shielding members 31A and 31B may also be possible as oneaspect of the second embodiment.

Third Embodiment

Next, a description will be given of the third embodiment of the presentinvention by referring to FIG. 5A, FIG. 5B, and FIG. 5C. FIG. 5A to FIG.5C are enlarged views of each connecting portion 35 of the plates 11 ofthe moving floor 12 applied to the third embodiment. In FIG. 5A to FIG.5C, the same reference signs are assigned to the same components asthose in FIG. 1A and FIG. 1B in terms of configuration or function, andduplicate description is omitted.

As shown in FIG. 5A to FIG. 5C, each connecting portion 35 includes ajoint 36, a pair of shafts 37, and a restricting member 38. The joint 36links two adjacent plates 11 together. The pair of shafts 37 rotatablysupport both ends of the joint 36 at both notches 39 provided at bothedges of each plate 11. Then the each restricting member 38 regulatesthe rotation of each joint 36 so as to allowing bending of the plates 11towards the bed while restricting bending of the plates 11 to theopposite side.

The connecting portion 35 configured as described above is provided ateach gap between adjacent two plates 11. Thus, when the stress F isapplied to the plate 11 shown in FIG. 5A, the two restricting members 38provided on both sides of this plate 11 give the reaction force f toprevent the joint 36 from rotate in the direction that the plates 11about to displace downward with respect to the adjacent two plates 11 onboth sides. As a result, the moving floor 12 is given high mechanicalrigidity so that the horizontal floor surface does not deform to a largeextent even when a technician or a patient rides thereon.

At the corner of the tunnel shape of the moving floor 12 as shown inFIG. 5C, it is possible for the plates 11 adjacent to each other to bendas a whole with the shaft 37 as the center. Similarly, a curved surfacecan be formed also in the tunnel-shaped arch portion without stress.

Although a block member provided on the lower side of the notch 39 ofeach plate 11 is illustrated as each restricting member 38, eachrestricting member 38 is not particularly limited to such an aspect. Anystructure that prevents the joint 36 for the plate 11 from bendingtowards the outside of the moving floor 12 can be used as therestricting member 38.

In the particle beam treatment apparatus 10 of the third embodiment, itis required that the joints 36 of the moving floor 12 are allowed tobend the plates 11 as a whole to the bed side and the bending to theopposite side is restricted. Thus, the particle beam treatment apparatus10 unequipped with the tunnel structure 16 may also be possible as oneaspect of the third embodiment. Additionally, the particle beamtreatment apparatus 10 in which the moving floor 12 is not composed ofthe separate bodies 17A and 17B may also be possible as another aspectof the third embodiment. Further, the particle beam treatment apparatus10 in which the moving floor 12 is unequipped with the shielding members31A and 31B may also be possible as still another aspect of the thirdembodiment.

According to the particle beam treatment apparatus of at least one ofthe above-described embodiments, a treatment space is widely formed byproviding the tunnel structure, and it is possible to improve generalversatility and robustness by shielding the gap of the moving floorand/or improving its mechanical rigidity.

Some embodiments of the present invention have been described above.These embodiments have been presented as examples. There is no intentionto limit the scope of the invention. These embodiments can also beimplemented in other various modes, and variously omitted, replaced,changed, and combined without departing from the gist of the invention.The embodiments and their variations are encompassed by the scope andgist of the invention. Likewise, these embodiments and variations areencompassed by the invention described in the claims and its range ofequivalence.

What is claimed is:
 1. A particle beam treatment apparatus comprising: arotating gantry configured to axially rotate in a state where a bedfixed to a stationary system is disposed inside the rotating gantry andan irradiation port of a beam is fixed to a body of the rotating gantry;a tunnel structure configured to have at least a horizontal floorsurface and have an internal space in which at least a part of the bedis accommodated; a moving floor configured to be formed by bendablyjoining a plurality of plates to each other in an annular shape suchthat the internal space is continuous from the tunnel structure, androtate together with the rotating gantry in a state where theirradiation port penetrates the moving floor; wherein the moving flooris composed of at least two separate bodies, respective edges of whichdivide connection of the plurality of plates at a portion which theirradiation port penetrates; a shielding member including a roll and asheet, is provided between the irradiation port and an edge portion ofeach of two separate bodies interposing the irradiation port, and isconfigured to shield a gap formed between the irradiation port and theedge portion; wherein a tip of the sheet is connected to one of theirradiation port and the edge portion while the roll is provided atanother of the irradiation port and the edge portion; and one side ofthe sheet being opposite to the tip is wound around the roll such thatthe roll is rotatably biased in a winding direction of the sheet.
 2. Theparticle beam treatment apparatus according to claim 1, wherein one endof the moving floor is engaged with a first rail, which is supported bythe stationary system and includes a closed track substantially matchingin vertical cross-sectional shape with the tunnel structure; and anotherend of the moving floor is engaged with a second rail, which is disposedto face the first rail such that the irradiation port is interposedbetween the first rail and the second rail.
 3. The particle beamtreatment apparatus according to claim 1, wherein the at least twoseparate bodies include traveling mechanisms for independently travelingthe respective closed tracks of the first rail and the second rail. 4.The particle beam treatment apparatus according to claim 1, wherein boththe tip and the roll of the sheet are connected to the edge portion ofeach of the two separate bodies to shield a gap formed between the eachedge portion of the two separate bodies.
 5. The particle beam treatmentapparatus according to claim 1, the moving floor further comprising: ajoint configured to link two of the plurality of plates adjacent to eachother; a pair of shafts configured to rotatably support both ends of thejoint at respective notches provided at both edges of the plates; and arestricting member configured to regulate the rotation of the joint toallow bending of the plurality of plates towards the bed and to restrictbending of the plurality of plates towards a side opposite to the bed.